Multi-Phase-field modeling of coupled corrosion-fatigue degradation in metallic materials

Stress corrosion cracking (SCC) and fatigue are key threats to metallic structures, and their coupling accelerates damage by promoting crack initiation and growth under cyclic loading in corrosive environments, often causing premature failures. This is critical in high-safety, high-cost systems, such as offshore turbines, nuclear piping, prestressed bridges, and aerospace components. Predictive tools for combined SCC and fatigue remain limited, as conventional approaches treat them independently, leading to conservative or unsafe performance estimates. In this work, a multi-phase-field chemo-mechanical framework is proposed to model the coupled interaction between corrosion and fatigue. Specifically, two phase-fields are employed: one for corrosion front evolution, including pitting and SCC, and another for fatigue crack initiation and growth, including the pit-to-crack transition. Mechanical straining acts as an electrochemical driving force, accelerating corrosion under cyclic loading. The formulation is implemented using the finite element method with implicit time integration, with displacements, phase-fields, and ionic concentration as primary variables. A series of numerical studies demonstrates the bidirectional coupling between corrosion and fatigue. Pre-existing corrosion is shown to reduce mechanical stiffness, lower fracture strength, eliminate the fatigue crack initiation phase, and significantly shorten fatigue lifetime. Conversely, fatigue-induced cracks act as preferential pathways for corrosive species, accelerating corrosion front advancement and redirecting corrosion propagation along crack paths. High-cycle fatigue simulations further reveal a corrosion-induced downward shift of S-N curves, in qualitative agreement with experimental observations reported in the literature. Overall, the proposed framework captures key qualitative mechanisms governing corrosion–fatigue interaction across different loading regimes, providing a physics-based tool for predicting damage evolution, identifying regions prone to premature failure, and supporting durability assessment and maintenance planning of metallic structures exposed to aggressive environments. The corresponding source code in this study is openly available at https://doi.org/10.25835/2czo4jvl to support further research.